Question

A terrestrial telescope has three lenses: an objective, an erecting lens, and an eyepiece.
(a) Does the erecting lens (1) increase the magnification, (2) increase the physical length of the telescope, (3) decrease the magnification, or (4) decrease the physical length of the telescope? Explain.
(b) This terrestrial telescope has focal lengths of 40 cm, 10 cm, and 5.0 cm for the objective, erecting lens, and eyepiece, respectively. What is the magnification of the telescope for an object at infinity?
(c) What is the length of the telescope barrel?